1. Field of the Invention
The present invention relates to a color image processing apparatus.
2. Related Background Art
In the conventional color digital image processing that is undertaken in digital color copying machines, digital color facsimile equipment and the like, full color images are obtained by using four colored inks of yellow, magenta, cyan and black in accordance with a subtractive color mixing process.
With respect to the black-color portions of a document, it is necessary to selectively use the black that is formed by superposing the three colors of yellow, magenta and cyan and the black that is formed by using the black ink alone.
In the undercolor removal (UCR) process which is conventionally employed in printing and the like, the minimum values of yellow, magenta and cyan are calculated as the black color, and the amount of each colored ink is reduced in a specific ratio with that reduced portion being replaced by the black ink.
This process makes it possible to reproduce a black whose density is greater than the black formed by superposing yellow, magenta and cyan, and the amounts of yellow, magenta and cyan inks used can thus be reduced.
However, if all the black portions are replaced by the black ink (100% UCR) as in the case of the above-described conventional apparatus, the quality of the image becomes degraded, so that it is impossible to realize 100% UCR.
Accordingly, an arrangement is made in which a small amount of each of the yellow, magenta and cyan is left. However, there is still a problem in that the remaining inks are scattered in the black character portions, and this scattering of the colored inks is noticeable, deteriorating the quality of the black characters.
A method of overcoming such problems is disclosed in U.S. Pat. No. 4,700,399 assigned to the assignee of this application. This application discloses a structure in which the proportion of undercolor removal carried out at the edge of a color image is increased and the quantity of the black ink is increased here to emphasize the edge.
Accordingly, a primary object of the present invention is to provide an image processing apparatus which is capable of performing efficient discrimination of character portions, thereby overcoming the above-described drawbacks of the prior art.
Another object of the present invention is to provide an image processing apparatus which is capable of preventing any downgrading of the quality of characters in a color image.
Still another object of the present invention is to provide an image processing apparatus which is capable of preventing the bleeding of characters in a color image to the peripheral portions thereof.
To these ends, according to one aspect of the present invention, there is provided a color image processing apparatus for digitally reading a color document and effecting digital printing, the color image processing apparatus comprising: character region extracting means for extracting a character region of said color document; black portion extracting means for extracting a black portion of said color document; and single black color processing means for processing a single black color only with respect to a region which falls within the character region and the black portion in the color document.
A further object of the present invention is to provide an image processing apparatus which is capable of detecting the continuation of a line in a character portion to favorably distinguish the character portion.
To this end, according to another aspect of the invention, there is provided an image processing apparatus comprising: input means for inputting image data; means for detecting an amount of change in the density of a block of mxc3x97n picture elements; two-valuing means for two-valuing the picture elements within the picture element block; and succession detecting means for detecting the succession of the two-valued picture elements within the picture element block.